1. Field of the Invention
The present invention relates to a slide guide device. More specifically, it relates to a device used in a machine for measuring a minute displacement with a high accuracy, such as a surface roughness measuring machine and a roundness measuring machine.
2. Description of Related Art
Typical machines for measuring a minute displacement with a high accuracy (e.g. a surface roughness measuring machine and a roundness measuring machine) requires a highly accurate motion mechanism for moving an object to be measured or a measurement tool. Accordingly, a slide guide device suitable for improving the accuracy is used for such a motion mechanism.
A slide guide device can enhance the positioning accuracy of a slider on motion axis line, and face rigidity and vibration damping capability of a guide surface by employing a slide movement that accompanies a solid-contact (i.e. contact between solids). In order to enhance the positioning accuracy of a slider along the motion axis line of the slide guide device, it is preferable that a friction resistance on the slide surface is small and the slide movement is smooth. Accordingly, the slide guide device is often provided by an oil-lubricated slide guide device in which a pair of slide surfaces to be slid are not mutually solid-lubricated but are lubricated at an interface therebetween with the use of lubricating oil, thereby reducing the friction coefficient and, consequently, the friction resistance.
It should be noted that, when the thickness of an oil film between the relatively-moving slide surfaces is increased to eliminate the mutual solid-contact (i.e. fluid lubrication), the friction coefficient can be reduced toward zero. However, a face-to-face dimension between the pair of slide surfaces widens in accordance with an increase in the thickness of the oil film, so that an accuracy in the direction of the motion axis (i.e. a guide direction) is deteriorated in the fluid lubrication. Further, when the thickness of the oil film increases, the thickness is likely to be fluctuated due to the load applied, thereby lowering the rigidity as a guide. Accordingly, the fluid lubrication is not suitable for a guide device that requires higher rigidity and damping capability.
In order to provide a highly accurate slide guide device, in addition to the above-described deterioration in the positioning accuracy due to the friction resistance at the slide portion, the moment generated to the slide portion due to the friction resistance and accompanying change in the attitude (positional error) have been studied.
For instance, Patent Literature 1 (JP-B-61-17613) or Patent Literature 2 (JP-A-62-241629) discloses a slide guide device for moving a slider along a guide body, the slide guide device including a pair of slide surfaces respectively on front and back sides of the guide body and a pair of slide pads provided to the slider with the guide body interposed therebetween, the pair of slide pads being slid on the pair of slide surfaces. In order to move the slider, a drive unit such as a ball screw shaft is used.
In the above arrangement, it is known that, when a centroid of the slide is misaligned with a center of the drive force, a moment is generated to the slider during acceleration or deceleration of the slider.
Further, when the resultant force of the friction resistance between the pair of surfaces and the pair of slide pads of the slide guide device is misaligned with the center of the drive force, the moment is generated not only during the acceleration/deceleration of the slider but also during a movement at a constant speed.
When the slider causes a rotation being affected by the moment of the slider, unnecessary displacement occurs to a measurement piece and the like supported by the slider, so that a sufficiently high accuracy cannot be obtained even with the use of the highly accurate slide guide device.
In order to deal with the above problem, Patent Literature 1 employs a dynamic pressure slide system (i.e. boundary lubrication where the solid-contact is maintained while lubricating oil is supplied) for one of the pair of slide pads, and a static pressure system (a system receiving the pressure by oil film) for the other of the pair of slide pads, and the hydraulic pressure of the slide pad of the static pressure system is controlled to be balanced with a contact face pressure of the slide pad of the dynamic pressure system, thereby restraining the moment from being generated to the slider. Then, a guide surface on which the slide pad of the dynamic pressure system slides is defined as a reference guide surface to ensure a guidance accuracy to avoid an influence of fluctuation of the thickness of the oil film between the slide pad of the static pressure system and the corresponding guide surface.
Further, in Patent Literature 2, one of the pair of slide pads is provided by the dynamic pressure system and the other of the pair of slide pads is provided by the static pressure system, and the pair of slide pads are provided at both ends in the movement direction of the slider, so that a compensation operation of the slide pads for the change in the attitude of the slider by control of the slide pad of the static pressure system can effectively work.
The slide guide devices according to the above-described Patent Literatures 1 and 2 employ the dynamic pressure system and the static pressure system for the pair of slide pads, so that the moment can be restrained from being generated to the slider due to the friction resistance of the slide pads.
However, in the slide guide devices according to Patent Literatures 1 and 2, the hydraulic pressure supplied to the slide pad of the static pressure system has to be intricately adjusted and maintained in accordance with a contact face pressure of the slide pad of the dynamic pressure system, and a complicated pipe system is also required. In addition, since a distance to a guide surface is measured for feedback control in order to keep the attitude of the slider in Patent Literature 2, the control system becomes necessarily complicated.
As described above, the moment is inevitably caused on the slider of the typical slide guide devices due to the friction resistance, thereby possibly lowering the accuracy. On the other hand, in order to provide a solution for the above deficiencies, the arrangement of the device necessarily becomes complicated.